It is known to use an inflatable vehicle occupant protection device, or air bag, to help protect a vehicle occupant in the event of a vehicle collision. The air bag is inflated by inflation fluid from an actuatable air bag inflator. The inflator may include a pyrotechnic gas generant, a stored gas supply, or a combination of stored gas and pyrotechnic material for heating the stored gas. The inflator is actuated in response to a signal indicative of vehicle deceleration of at least a predetermined magnitude. The inflation fluid is then directed from the inflator into the air bag to inflate the air bag.